Various diseases today require a treatment which involves administration of peptide-, protein-, and nucleic acid-based drugs, particularly the transfection of nucleic acids into cells or tissues. The full therapeutic potential of peptide-, protein-, and nucleic acid-based drugs is currently compromised by their limited ability to cross the plasma membrane of mammalian cells, resulting in poor therapeutic efficacy.
RNA molecules have the capacity to act as potent modulators of gene expression in vitro and in vivo and therefore have great potential as nucleic acid based drugs. These molecules can function through a number of mechanisms utilizing either specific interactions with cellular proteins or base pairing interactions with other RNA molecules. RNA interference is a process of gene silencing that plays an important role in development and maintenance of the genome. The RNAi pathway is complex. It is initiated by the enzyme dicer which cleaves double stranded RNA (dsRNA) into fragments. An RNA-induced silencing complex (RISC) is then formed by base pairing between complementary mRNA and the guide strand of each new fragment. The passenger strand of each fragment is degraded. This formation of the RISC complex leads to translational silencing or degradation of the complementary mRNA by the endonuclease argonaute. Argonaute is the catalytic component of the complex. The short fragments are known as small interfering RNA (siRNA) and microRNA (miRNA) for example. Modulation of gene expression via RNA effector molecules, such as siRNA, has great therapeutic potential as the modulatory complexes formed, be they RNA-protein complexes or RNA-RNA complexes, are often highly specific. However, in order for such RNA effector molecules to modulate gene expression they must be present in the cell's cytoplasm to enter into the RISC Complex.
The delivery of exogenous oligonucleotides such as RNA molecules and other membrane impermeable compounds into living cells is highly restricted by the complex membrane systems of the cell. Typically, molecules used in antisense and gene therapies are large, negatively charged and hydrophilic molecules. These characteristics preclude their direct diffusion across the cell membrane to the cytoplasm. For this reason, the major barrier to the therapeutic use of oligonucleotides for modulation of gene expression is the delivery of the oligonucleotide to the cytoplasm. Transfection agents used in the art today typically comprise peptides, polymers, and lipids of a cationic nature as well as nano- and microparticles. These transfection agents typically have been used successfully only in in vitro reactions as the cationic nature of these systems, while facilitating both cell binding and binding of the oligonucleotide, renders them ineffective or toxic in vivo. Furthermore, the cationic charge of these systems causes interaction with serum components, which causes destabilization of the oligonucleotide-transfection reagent interaction and poor bioavailability and targeting. When transfecting nucleic acids in vivo further requirements have to be fulfilled. For example, the complex should not interact with parts of the complement system of the host. Additionally, the complex should protect the nucleic acid from early extracellular degradation by ubiquitously occurring nucleases. Furthermore, the carrier should not be recognized by the adaptive immune system (immunogenicity) and should not stimulate an acute immune response.
Although high transfection efficiencies are possible in vitro, achieving similar extents of transfection without toxicity is difficult in vivo. In general, exogenous unmodified nucleic acid molecules, particularly viral nucleic acids, introduced into the cell induce an innate immune response which results in cytokine and interferon (IFN) production and ultimately cell death. It is of great interest for therapeutics, diagnostics, reagents and for biological assays to be able to deliver a nucleic acid, e.g., a ribonucleic acid (RNA), into a cell, such as to cause intracellular translation of the nucleic acid and production of the encoded protein instead of generating an innate immune response. This delivery issue is currently the major prohibitive factor for the application of nucleic acid-based drugs, particularly RNA based therapeutics, in vivo. Thus, there remains a need for an effective delivery system for efficiently delivering nucleic acid-based drugs, particularly RNA based therapeutics, to cells and tissues. The present invention provides compositions and methods for the delivery and release of an oligonucleotide to a cell.